Process of simultaneously crimping and reacting drawn nylon fibers with hot alcoholic formaldehyde solution



United States Patent 3,370,912 PROCESS OF SIMULTANEOUSLY CRIMPING ANDREACTING DRAWN NYLON FIBERS WITH HOT ALCOHOLIC FORMALDEHYDE SOLUTIONConrad Georg Baumann, Zurich, Switzerland, assignor to Heberlein PatentCorporation, New York, N.Y., a corporation of New York No Drawing. FiledMar. 16, 1965, Ser. No. 440,323 7 Claims. (Cl. 8115.5)

This invention relates to a method for treating polyamide fabrics, andmore specifically, it relates to a method for chemically crimpingpolyamides.

For purposes of this application the term textile material or fabricshall be understood to include fabrics and textile materials of allkinds, including fibers, filaments, yarns, threads, and any manner ofknit or woven fabrics as well as non-woven or felted fabrics.

It is known that polyamide textile materials can be chemically crimpedby the formation of asymmetrical, incomplete cross-linkings betweenamide groups of polyamide molecules. This cross-linking has beenachieved by methoxylation of the polyamide, sulfonation of themethoxymethylate, and finally the formation of sulfide bonds between themolecules. Subsequently, the treated polyamide threads are subjected toa swelling treatment to at least double the volume of the originalthread, and spontaneous crimping takes place. The treated fibers arethen dried.

While the foregoing method is capable of producing certain interestingcrimping effects, it has a number of serious disadvantages. It calls forthree chemical reactions prior to the swelling treatment and requiresrelatively expensive sulfur compounds, such as thiourea. These sulfurousmaterials, moreover, not only produce disagreeable odors duringprocessing but the odors are also diflicult to remove from the treatedfabric.

This invention provides a considerably simpler and cheaper process forobtaining crimping effects in polyamide materials. Such crimping isgenerally superior to the crimping effects obtainable by the prior artprocesses.

This invention also provides a novel chemically crimped polyamidematerial.

Briefly, the process of this invention spontaneously crirnps and shrinkspolyamide fabrics by treating them in alcoholic formaldehyde solutionsin the presence of an acid catalyst at temperatures at least about 50 C.for times not significantly in excess of ten minutes. This process thusprovides novel crimped polyamide fibers and filaments and providesfabrics having increased density with a softer, more desirable hand.

In practicing this invention it is necessary that the polyamide fibersor filaments be drawn prior to treatment with the alcoholicformaldehyde. It will be understood that a drawn polyamide fiber is onewhich has been placed under tension so as to increase its originallength significantly. In practicing this invention the polyamide fibersshould have been drawn to at least 250% of their original length, andthey should preferably be drawn to 300% or more of their originallength.

While the drawing of nylon per se does not form a part of thisinvention, it is hypothesized that such a drawing of the polyamidefilaments orients the crystals or crystal-like structures in the fibers.In any event, if undrawn polyamide-containing fabrics are subjected tothe treatment of this invention, the fibers have a tendency to becomevery stretchy and elastic and the desirable properties of crimpedmaterial are lost.

It is especially preferred to treat textile fabrics containing nylon 6,that is, polymers of e-aminocaproic acid.

In the process of this invention, it is believed that the amide groupsof the polymers are methoxylated. Contrary to the prior art processes,however, the crimping produced by this invention does not appear to bebased on differential cross-linking, but rather appears to rise fromsubstitution in the secondary amino group of the polyamides. Apparently,the number of sites for the formation of hydrogen bridges betweenadjacent molecules is reduced and the crystal structure or texture ofthe fiberforming material is changed. This appears to be the cause ofthe crimping or shrinking.

Where yarns and threads are treated according to this invention, astrong crimping effect is obtained. Where woven and knit goods aretreated, considerable shrinkage occurs and the density of the materialis increased with consequent improvement of the hand. Moreover, whendrawn polyamides are treated acccording to this invention the electricalconductivity of the fabric is enhanced and the propensity of thematerial to retain static electric charges is reduced. Not only are thehand and electric conductivity improved, but in addition the dyeabilityof the polyamide is enhanced. Moreover, the tearing strength of thepolyamide filaments and fibers is surprisingly increased.

The treatment bath used in this process must furnish formaldehyde forinteraction with the polyamide. Formaldehyde may be added directly tothe alcoholic treatment bath or a substance roducing formaldehyde underthe reaction conditions can also be used in the bath. A preferredmaterial for use in the treatment bath is paraformaldehyde.

The treatment bath should contain a relatively high concentration offormaldehyde. Generally, it is preferred that the bath contain at leastabout by weight of formaldehyde, and the formaldehyde can be present inconcentrations as high as the saturation point of the formaldehyde inthe particular alcohol.

The formaldehyde is used in an alcoholic medium. The alcohols suitablefor use in the practice of this invention are the lower aliphaticmonohydroxy alcohols. Generally lower aliphatic alcohols containing fromabout 1 to about 6 carbon atoms are suitable. Preferred alcohols aremethanol, ethanol, and isopropanol.

The temperature. of the treatment should be at least about 50 C. inpracticing this process. The upper temperature limit of the process isusually determined by the atmospheric boiling point of the alcohol usedin the bath. With the readily available alcohols, it is preferred tocarry out the process at temperatures in the range of from about 60 toabout C.

The time of treatment is very important in this process. While thetreatment time will vary inversely as the temperature of the treatment,the time should be restricted to an upper limit of about 10 minutes. Theuse of a longer time will adversely affect the finished product, andsome of the polyamide properties will be degraded by excessive treatmentintervals. For example, treatment times on the order of 20 minutesresult in partial fusion of the fabric and are very detrimental to thehand. Moreover, treatment of the fabric for as long as 20 minutes causespartial dissolution of the polyamide material and adversely affects thestrength thereof. It has been found that a treatment of 5 minutes orsomewhat less is generaly adequate to produce the desired results. It ispreferred in this process to treat the polyamide materials for a time onthe order of from about 5 to about 10 minutes.

The treatment bath must also contain an acid catalyst. Suitable acidcatalysts are ammonium bromide, calcium chloride, phosphoric acid,p-toluene sulfonic acid, mono-, di-, and trichloroacetic acid.Dicarboxylic acids such as maleic acid are excellent catalysts. Apreferred catalyst is oxalic acid.

After the treatment of the polyamide fabric has been carried out, theformaldehyde-containing solution should be removed from contact with thematerial. One of the most effective ways to remove the formaldehydesolution from the material is to wash it with an alcohol, convenientlythe same alcohol used as the solvent in the solution, and then to washall the alcohol out with cold water. After washing the treatmentsolution out of the material and drying, the material will then besuitable for further use or processing.

The following examples are given to illustrate some embodiments of thisinvention and not to indicate the entire scope of the invention, thescope being determined by the claims appended hereto.

Example I A solution is prepared by dissolving 250 g. ofparaformaldehyde (trioxymethylene) in 300 ml. of ethanol with vigorousstirring at a temperature of 65 C. After the formaldehyde is dissolved,14.3 g. of anhydrous oxalic acid is added as a catalyst and the solutionis filtered.

The temperature of the solution is raised to 80 C. and a skein of drawnnylon 6 yarn is immersed in the bath for minutes to spontaneously crimpthe yarn. Subsequently the yarn is thoroughly washed with ethanol, thenwith cold water, and dried.

This treatment results in a powerful crimping of the yarn and itstensile strength is found to be more than twice that of the originalyarn.

Example II The treatment solution is prepared by saturating 300 ml. ofmethanol with paraformaldehyde at a temperature of 65 C. and adding 15g. of oxalic acid as a catalyst.

I The solution is then filtered.

Example III The treatment bath is prepared by saturating 300 ml. ofisopropanol with formaldehyde at a temperature of 65 C. and subsequentlyadding 15 g. of oxalic acid as a catalyst. The solution is thenfiltered.

The bath'is maintained at 65 C. and a woven fabric of drawn nylon 6 yarnis immersed in the bath for 10 minutes, washed thoroughly with ethanoland then with cold water, and dried.

After'this treatment the fabric is considerably shrunken and exhibits animproved hand.

What is claimed is:

1. A process for crimping polyamide textile materials which comprisestreating nylon textile fibers, which have been drawn to at least 250% oftheir original length and consisting essentially of a polymer ofe-aminocaproic acid,

by immersing said fibers in a solution of at least 75% by weight offormaldehyde in a monohydric lower aliphatic alcohol containing an acidcatalyst at a temperature of from at least about C. to the temperatureat which said alcohol boils at atmospheric pressure for a maximum ofabout 10 minutes, said time being inversely related to said temperature,until said fibers simultaneously shrink and become crimped.

2. A process for crimping polyamide textile materialsv which comprisestreating nylon textile fibers, which have been drawn to at least 250% oftheir original length and consisting essentially of a polymer ofe-aminocaproic acid, by immersing said fibers in a solution of at leastby Weight of formaldehyde in a monohydric lower aliphatic alcoholcontaining an acid catalyst at a temperature of from at least about 50C. to the temperature at which said alcohol boils at atmosphericpressure for a maximum of about 10 minutes, said time being inverselyrelated to said temperature, until said fibers simultaneously shrink andbecome crimped, and subsequently washing the crimped nylon to remove thesolution.

3. A process for crimping polyamide textile materials which comprisestreating nylon textile fibers, which have been drawn to at least 250% oftheir original length and consisting essentially of a polymer ofe-aminocaproic acid, by immersing said fibers in a solution of at least75% by weight of formaldehye in a monohydric lower aliphatic alcoholcontaining an acid catalyst at a temperature of from at least about 50C. to the temperature at which said alcohol boils at atmosphericpressure for from about 5 to about 10 minutes, said time being inverselyrelated to said temperature, until said fibers. simultaneously shrinkand become crimped.

4. The process of claim 1 wherein the alcohol is se lected from thegroup consisting of methanol, ethanol, and isopropanol.

5. The process of claim 1 wherein the catalyst is oxalic acid.

6. A process for crimping polyamide textile materials which comprisestreating nylon textile fibers, which have been drawn to at least 250% oftheir original length and consisting essentially of a polymer ofe-aminocaproic acid, by immersing said fibers in a solution of at least75% by weight of formaldehyde in a monohydric lower aliphatic alcoholcontaining an acid catalyst at a temperature of from about 60 to aboutC. for from about 5 to about 10 minutes, said time being inverselyrelated to said temperature, until said fibers simultaneously shrink andbecome crimped.

7. A crimped polyamide textile material prepared according to theprocess of claim 1.

References Cited UNITED STATES PATENTS 2,441,085 4/1948 Schneider 8115.5

NORMAN G. TORCHIN, Primary Examiner;

H. WOLMAN, Assistant Examiner.

1. A PROCESS FOR CRIMPING POLYAMIDE TEXTILE MATERIALS WHICH COMPRISESTREATING NYLON TEXTILE FIBERS, WHICH HAVE BEEN DRAWN TO AT LEAST 250% OFTHEIR ORIGINAL LENGTH AND CONSISTING ESSENTIALLY OF A POLYMER OFE-AMINOCAPROIC ACID, BY IMMERSING SAID FIBERS IN A SOLUTION OF AT LEAST75% BY WEIGHT OF FORMALDEHYDE IN A MONOHYDRIC LOWER ALIPHATIC ALCOHOLCONTAINING AN ACID CATALYST AT A TEMPERATURE OF FROM AT LEAST ABOUT50*C. TO THE TEMPERATURE AT WHICH SAID ALCOHOL BOILS AT ATMOSPHERICPRESSURE FOR A MAXIMUM OF ABOUT 10 MINUTES, SAID TIME BEING INVERSELYRELATED TO SAID TEMPERATURE, UNTIL SAID FIBERS SIMULTANEOUSLY SHRINK ANDBECOME CRIMPED.